The invention disclosed herein pertains to a method and apparatus for applying and sealing labels to containers and to the containers resulting from treatment with the method.
A machine for applying and sealing labels to containers is described in U.S. Pat. No. 4,694,633. In this machine, each container is supported on a rotating disk so that the container rotates, as it is carried by a turntable, to serve as a mandrel about which the label is wrapped. At the start of container rotation, a vacuum bar is driven into juxtaposition with the container periphery. The vacuum bar attracts the leading end of a label and carries the label around the container sufficiently for the trailing end of the label to overlap the leading end. At this time, the overlapped ends are subjected to a heating element or a jet of hot air which seals the trailing end to the leading end of the label. The vacuum bar is then withdrawn. This leaves a free space between the label and the container so the label fits loosely on the container. Thus, the additional step of heat shrinking the entire label onto the container is required. The machine is only suitable for applying labels which are heat-shrinkable. Heating the entire surface of the label on the container is expensive and can result in wrinkles developing in the label. The machine is also not suitable for labeling prefilled aerosol cans which cannot be heated safely. Moreover, the thin suction bar and associated control mechanism are costly to manufacture and are vulnerable to damage.
Another machine for wrapping labels around rotating containers is disclosed in U.S. Pat. No 4,272,311. In this machine, containers are conveyed in a straight line past an application station where a web of labels is drawn from a supply roll. Adhesive is applied at the interface of the leading edge of the label and the container. The leading edge of the web is then pressed against the container by means of a revolving belt. The individual label is cut from the web only after the web is partially wrapped around the container. To provide time for cutting, the web is stopped with a clamping device and the label which is already in contact with the container is torn or cut from the web along a perforated web. The label is then continuously rotated by reason of being in contact with the belt until the label is completely wrapped around the container. The overlap region of the leading and trailing ends of the label can be joined by having previously applied adhesive to the trailing end of the label or the trailing end can be sealed to the leading end by applying heat to the overlapped region. One disadvantage of the machine is that the adhesive-coated label is not separated from the web until the label is partially wrapped around the container which requires that the web be stopped for severing the label. This is obviously disadvantageous in that the method is intermittent rather than continuous which results in its product output being low. When the machine is driven at higher speeds, there is not sufficient time allowed for a reliable fusion of the leading and trailing edges of the label to achieve a good seal. Consequently, applying adhesive to a large area on the inside of the label or to the outside of the container is often necessary. This is highly disadvantageous, particularly in the application of labels composed of thin and transparent film, for reasons of appearance. The known apparatus is not suitable for achieving high production rates of 40,000 to 80,000 bottles or cans per hour as is a common requirement in the beverage industry today.
U.S. Pat. No. 4,416,714 discloses applying an adhesive coated leading end of a label to a rotating container to effect wrapping of the label on the container. The label is secured by adhering the trailing end over the underlying leading end. Labels are fed, one at a time, to the containers from a vacuum drum. Heat shrinking of the edges of the label to the contour of the container is disclosed, but heat sealing the overlapped label ends in addition to having adhesive applied near the trailing end as is described herein is not disclosed.
Japanese Patent No. Sho 57-23620, published May 19, 1982, discloses wrapping a heat shrinkable label around a container and heat sealing the overlapping trailing and leading ends of the label. The top and bottom edges of the label are heat-shrunk to conform them to the contour of the container. A back-up bar is placed behind the overlapping ends, at least along the edges which extend over the contour, to allow pressing the overlapping ends together by a hot heat seal member or a cold member when the label ends are sealed with glue. There is no disclosure of how the heat sealing time can be held substantially constant for different container transport speeds as is described herein.